Conventional pure electrical vehicles (“EV”) are typically range-limited. The 2013 Tesla Model S electric vehicle provides a variety of battery systems of increasing capacity, and correspondingly increasing expense, of 40 kWh, 60 kWh and 85 kWh, with respective ranges of 160 miles, 230 miles, and 300 miles. However, given the expense of high-range battery systems, many EVs have more modest ranges. As one example, the 2013 Nissan Leaf® electric vehicle has a range of “up to” about 75 miles on a single charge from its more conventionally-sized 24 kWh Lithium-Ion battery system manufactured by Automotive Energy Supply Corporation (AESC).
Unfortunately, the maximum potential range is often not achieved in the manner that EVs are typically driven and the actual range a moving target. The operative range of an EV is complicated by the numerous environmental variables (e.g., weather, temperature, traffic, etc.) and vehicle variables (e.g., use of air conditioning/heating, lights, etc.) so that the actual range on any given day may vary markedly from the range of the same car on prior commutes between the same points. FIG. 1 provides an example of such range variability for the Nissan Leaf® EV for the 2011/2012 model year. Even amongst governmental organizations, the estimated range for this specific vehicle cannot be agreed upon. The United States Environmental Protection Agency estimates the range of the Nissan Leaf® EV to be 73 miles, whereas the United States Federal Trade Commission, estimates the range of the Nissan Leaf® EV to be between 96-110 miles and the New European Driving Cycle estimates the range of the Nissan Leaf® EV to be about 109 mi. Third-party sources indicate that the range available from a single charge can vary up to 40% in real-world situations depending on driving style, load, traffic conditions, weather (i.e. wind, atmospheric density), and accessory use. Nissan itself determined that the range of the Nissan Leaf® EV, in a “worst case” scenario, could be only 47 miles on a full charge.
To further illustrate this variability, FIG. 1 shows a table summarizing the ranges of a Nissan Leaf® EV under a number of scenarios tested using EPA's L4 test cycle. When cruising at a constant speed (an ideal condition) at 38 mph at a temperature of 68° F., with the air conditioner off, the range is 138 miles over a drive duration of 3 hours, 38 minutes. Driving in city traffic at 24 mph at a temperature of 77° F., with the air conditioner off, yields a range of 105 miles over a drive duration of 4 hours, 23 minutes. Driving on the highway at 55 mph at a temperature of 95° F., with the air conditioner in use, yields a range of 70 miles over a drive duration of 1 hour, 16 minutes. Driving in winter stop-and-go traffic at 15 mph at a temperature of 14° F., with the heater on, yields a range of 62 miles over a drive duration of 4 hours, 8 minutes. Driving in heavy stop-and-go traffic at 6 mph at a temperature of 86° F., with the air conditioner on, yields a range of 47 miles over a drive duration of 7 hours, 50 minutes. Notably, these results assume a driving speed of no more than 55 mph and the effect of wind resistance (and vehicle drag) increases with increasing speed, further limiting the range of the EV. By way of comparison, United States Department of Energy studies concluded that, for conventional internal combustion vehicles, the average car will be at its advertised MPG at 55 mph, but as the speed increases such vehicle is about 3% less efficient at 60 mph, 8% less efficient at 65 mph, 17% less efficient at 70 mph and 23% less efficient at 75 mph.
This variability gives rise to a fear in the driver of EVs that their vehicle may have insufficient range to reach the intended destination and may leave them stranded on the roadside, a fear now referred to as “range anxiety”.
A variety of conventional charging sources are available to ease this anxiety. Conventional 120V household sockets and extension cords may be provided at common destinations (e.g., work parking lot, parking structures, residences, etc.), but this option can pose risks if used incorrectly, presents various limitations, and takes considerable time (e.g., 6 to 8 hours). Distributed charging stations are also being deployed by various governmental and/or private entities to facilitate greater utilization of EVs by effectively increasing their native ranges and/or by reducing range anxiety. By way of example, Tesla has developed and built a number of electric vehicle charging stations (e.g., a Tesla EV “Supercharge” station) along selected high volume traffic corridors. Other proposed solutions have included “swappable” battery systems available at battery exchange centers (see, e.g., U.S. Published Patent Application No. 2010/071979).
However, despite the growth of these enhancements to the use of EVs, the problem of range anxiety and, more particularly, actual depletion of EV batteries in the midst of a trip, remains unresolved.
To address the actual problem of stranded EVs, specialized road-side assistance vehicles have been proposed to use a master battery and converter to power EVs (see, e.g., U.S. Published Patent Application No. 2012/0271758 A1). This solution addresses the problem, but itself presents new problems, such as availability and arrival time.